1. Field of the Invention
This invention relates to a sheet feeding apparatus for feeding and conveying sheets (paper leaves such as originals, transfer paper, photosensitive paper, electrostatic recording paper, thermosensitive paper, printing paper, OHP sheets, envelopes and postcards) such as cards and thin paper leaves piled in various sheet-using apparatuses such as image forming apparatuses including rotary type cameras, facsimile apparatuses, printing machines, copying machines, printers, word processors, etc. and other apparatuses such as automatic original feeding apparatuses, punching machines and paper binding machines one by one to a sheet processing portion such as an image forming portion, an exposure portion and a processing portion.
2. Related Background Art
As one of the sheet separating mechanisms of sheet feeding apparatus for separating and conveying piled sheets one by one, there is known a mechanism using a pair of comb-toothed rollers.
This mechanism is such that two comb-toothed rollers formed with comb-tooth-like grooves in the outer peripheral portion thereof are disposed in opposed relationship with each other substantially in parallelism to each other with the concave surfaces and convex surfaces of their grooves axially overlapping each other in non-contact with each other, and one of the two rollers is used as a feeding roller and the frictional force thereof with respect to a sheet is made great and the other roller is used as a separating roller and the frictional force thereof with respect to the sheet is made smaller than that of the feeding roller. The feeding roller is rotated in a forward feeding direction and the separating roller is rotated in a reverse feeding direction, and the sheet is fed to the nip portion between this pair of rollers. Thereby, even if a plurality of sheets are fed in overlapping relationship with one another, only the sheet which is in contact with the feeding roller is passed through the nip portion by the feeding force of the feeding roller rotated in the forward feeding direction, irrespective of the separating roller rotated in the reverse feeding direction, and the other sheets are reversely conveyed by the separating roller rotated in the reverse feeding direction and is prevented from coming into or being passed through the nip portion, whereby only that sheet which is in contact with the feeding roller is separated and conveyed.
There is also known a mechanism in which when sheets are separated and conveyed one by one, a movable guide plate provided at one side or both sides of the sheet to prevent skew feeding is moved and the side portion of a skew-fed sheet is pushed against the guide plate to thereby correct skew feeding, or a mechanism in which the skew feeding of a sheet being fed is detected by the use of a sensor and as required, a conveying roller is rotatively driven by an amount corresponding to the skew feeding to thereby forcibly effect correction.
FIG. 13A schematically shows the construction of a sheet feeding apparatus using a pair of comb-toothed rollers as a sheet separating mechanism.
sheets 200 are piled and set in a predetermined manner on a sheet supply tray 1. This sheet supply tray 1 is vertically controlled to a sheet supply position indicated by solid line and a standby position indicated by dots-and-dash line.
An upper guide plate 2 and a lower guide plate 3 together constitute a sheet conveying path. The sheet supply tray side of the lower guide plate 3 is downwardly bent forwardly of the fore end of the sheet supply tray 1 to provide a sheet leading end ramming plate portion 3a for uniformizing the position of the leading end surface of the sheets piled on the sheet supply tray 1.
A sheet feeding roller 4 picks up and feeds the sheets 200 piled and set on the sheet supply tray 1.
A pair of feeding roller and separating roller 5 and 6 are disposed downstream of the sheet feeding roller 4 with respect to the direction of sheet conveyance. The feeding roller 5 is an upper roller and the separating roller 6 is a lower roller.
The feeding roller 5 and the separating roller 6, as shown in the perspective view of FIG. 13B, are such that comb-toothed rollers formed with comb-tooth-like grooves in the outer peripheral portions thereof are disposed in opposed relationship with each other substantially in parallelism to each other with the concave surfaces and convex surfaces of the grooves thereof axially overlapping each other in non-contact with each other. The frictional force of the feeding roller 5 with respect to the sheet is made greater than the frictional force of the separating roller 6 with respect to the sheet.
Registration rollers 16 and conveying rollers 17 are successively disposed downstream of the pair of feeding roller and separating roller 5 and 6 with respect to the direction of sheet conveyance.
The sheet feeding roller 4 receives the transmission of motive power from a first motor M1 through a pulley 12, a belt 11, a two-step pulley 10, a belt 8 and a pulley 4a, and is rotatively driven in the clockwise direction of arrow which is a forward feeding direction.
Of the feeding roller 5 and the separating roller 6, the feeding roller 5 receives the transmission of motive power from the first motor M1 through the pulley 12, the belt 11, the two-step pulley 10, a belt 9 and a pulley 5a, and is rotatively driven in the clockwise direction of arrow A which is the forward feeding direction.
Also, the separating roller 6 receives the transmission of motive power from a second motor M2 through a pulley 13, a belt 7 and a pulley 6a, and is rotatively driven at the nip portion with the feeding roller 5 in the clockwise direction of arrow B which is a reverse feeding direction.
Of the feeding roller 5 and the separating roller 6, the feeding roller 5 is disposed on a movable chassis 21 pivotally movable about the support shaft of the two-step pulley 10. The reference numeral 20 designates a shaft provided on the upper side of the movable chassis 21, and the reference character 20a denotes a cam follower provided on one end side of this shaft 20. The reference numeral 19 designates an eccentric cam, and the movable chassis 21 is counter-clockwisely biased about the support shaft of the two-step pulley 10 by a biasing spring member, not shown, so that the cam follower 20a may be normally in contact with the lower surface portion of the eccentric cam 19. The reference numeral 27 denotes an adjusting knob for rotatively operating the eccentric cam 19.
The above-described adjusting knob 27, eccentric cam 19, can follower 20a, shaft 20, movable chassis 21, etc. together constitute a mechanism for changing the distance between the shafts of the feeding roller 5 and the separating roller 6.
That is, by the adjusting knob 27 being turned, the cam 19 is rotated and the motion of the cam is transmitted to the feeding roller 5 through the cam follower 20a, the shaft 20 and the movable chassis 21, and the vertical position of the feeding roller 5 is displaced, and the distance between the shafts of the feeding roller 5 and the separating roller 6 can be changed more or less to thereby adjust the amount of entry or the amount of gap of the feeding roller 5 relative to the separating roller 6 in accordance with the thickness of the sheet.
Thus, during non-sheet feeding, the sheet supply tray 1 is lowered to its standby position indicated by dots-and-dash line, and is downwardly spaced apart from the sheet feeding roller 4. In this state, the sheets 200 are piled and set on the sheet supply tray 1. The sheets 200 are sufficiently inserted until the leading end thereof strikes against the ramming plate portion 3a, whereby the position of the leading end surface of the sheets piled on the sheet supply tray 1 is uniformized.
On the basis of a sheet feed starting signal, the sheet supply tray 1 is moved upwardly and as indicated by solid lines, the upper surface of the leading end side of the sheets 200 piled on the sheet supply tray 1 is held in contact with the lower surface of the sheet feeding roller 4.
Thereupon, the uppermost sheet 22 of the piled sheets 200 is fed out (picked up) by the rotating sheet feeding roller 4, and arrives at the nip portion between the feeding roller 5 and the separating roller 6 while being guided by the upper guide plate 2 and the lower guide plate 3 and enters the nip portion.
The uppermost sheet 22 which has entered the nip portion is conveyed through the nip portion by the feeding force of the feeding roller 5 rotated in the forward feeding direction, irrespective of the separating roller 6 rotated in the reverse feeding direction, because the frictional force of the feeding roller 5 with respect to the sheet is greater than that of the separating roller 6.
Also, even if a plurality of sheets 22, 22', . . . are overlapping fed to the nip portion by the sheet feeding roller 4, only the sheet 22 of the double-fed sheets which is in contact with the feeding roller 5 passes through the nip portion by the feeding force of the feeding roller 5 rotated in the forward feeding direction, irrespective of the separating roller 6 rotated in the reverse feeding direction. The other sheets 22', . . . are reversely conveyed by the separating roller 6 rotated in the reverse feeding direction and is prevented from entering or passing through the nip portion and double feeding is thus prevented, whereby only the sheet 22 which is in contact with the feeding roller 5 is separated and conveyed.
The sheet 22 separated and conveyed by the pair of feeding roller and separating roller 5 and 6 passes the registration rollers 16 and the conveying rollers 17 and is fed to a sheet processing portion such as a reading portion, not shown. The registration rollers 16 determine the conveyance timing at which the sheet 22 is conveyed to the sheet processing portion, in conformity with the instructions from a control portion (CPU), not shown, and effect the conveyance of the sheet.
When sheets of different thicknesses are to be fed, the adjusting knob 27 is rotatively operated to thereby change the amount of entry or the amount of gap of the feeding roller 5 relative to the separating roller 6 at the nip portion between the feeding roller 5 and the separating roller 6, and set it to a predetermined sheet thickness. That is, the rotated position of the cam 19 connected to the adjusting knob 27 is changed, whereby the shaft 20 in contact with the cam 19 and the movable chassis 21 connected to the shaft 20 are moved to change the distance between the shafts of the feeding roller 5 and the separating roller 6, whereby said setting is effected and even sheets of different thicknesses can be conveyed while avoiding double feeding.
In the case of the above-described sheet separating mechanism, the distance between the shafts of the pair of comb-toothed rollers which are the feeding roller and the separating roller is adjustable so that normal separation may be done even if the thickness of the sheet changes.
However, there has been the problem that the above-mentioned adjustment must be manually effected to a proper position for each thickness of the sheets being fed and sheets of different thicknesses cannot be mixedly piled and processed.
Also, movable guide plates (not shown) provided at one side or both sides of the sheets are moved to prevent the skew feeding when the sheets are separated and conveyed one by one, and correction is effected with the side portions of the sheets rammed against the guide plates to prevent skew feeding.
Such a skew feeding correcting mechanism has been very cumbersome in that the positions of the guide plates must be changed when sheets of different widths are to be conveyed.
Also, a mechanism for detecting the skew feeding of a sheet being conveyed by the use of a sensor, and effecting rotative driving by an amount corresponding to the skew feeding by the use of a conveying roller as required to thereby forcibly correct the skew feeding has suffered from the disadvantage that the construction is complicated and sheets become wrinkled.